Magnetic properties and structural phase transition in ultrathin fcc Fe (111) and bcc Fe (111) films: first-principles study

TL;DR

This study uses first-principles calculations to explore the structural phase transition and magnetic properties of ultrathin Fe films, revealing a thickness-dependent transition from fcc to bcc structure and associated magnetic behavior.

Contribution

It provides detailed computational insights into the thickness-induced phase transition and magnetic characteristics of Fe(111) films, aiding substrate selection for experimental applications.

Findings

Structural phase transition from fcc to bcc at 23 monolayers.

Fcc films favor low-spin ferromagnetic state with ~1.0 μ_B per atom.

Magnetic anisotropy energy remains positive across fcc film thicknesses.

Abstract

The aim of this work is to investigate the structural and magnetic characteristics of Fe thin films with a triangular (hexagonal) lattice surfaces (fcc (111) and bcc (111)). The properties of these structures have been calculated using density functional theory (DFT) implemented in the full-potential local-orbital(FPLO) code. The results indicate a structural phase transition from fcc to bcc structure when the film thickness exceeds 23 Fe atomic monolayers. The considered fcc films prefer the low-spin ferromagnetic state with an average magnetic moment of about 1.0 $\mu_{B}$ per atom. This moment decreases with increasing film thickness until the critical thickness, where, after the structural transition to the bcc phase, it reaches a value close to that of bulk bcc Fe. Moreover, the values of the magnetic anisotropy energy are positive (perpendicular magnetic anisotropy) for the entire thickness range of films with fcc structure (in ferromagnetic low-spin state) and systematically decrease with increasing film thickness. The presented computational results explain the experimentally observed structural transition and may help to select appropriate substrates with suitable lattice parameters for the deposition of ultrathin Fe(111) films.